1. Technical Field
The present invention relates to organic light-emitting devices, and to organic light-emitting display apparatuses including the organic light-emitting devices.
2. Description of the Related Art
Organic light-emitting devices (OLEDs) are self-emitting devices that have advantages such as wide viewing angles, good contrast, quick response times, high luminance, and good driving voltage characteristics. OLEDs can also provide multicolored images. Thus, organic light-emitting devices have recently drawn attention.
An organic light-emitting device includes an anode, a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and a cathode, which are sequentially formed on a substrate. The HTL, the emission layer, and the ETL are formed of organic compounds. When a voltage is applied between the anode and the cathode of the organic light-emitting device, holes injected from the anode move to the EML via the HTL, and electrons injected from the cathode move to the EML via the ETL. These carriers, i.e., the holes and electrons, recombine in the EML to generate excitons. When the excitons drop from an excited state to the ground state, light is emitted.
The luminescent material is the most important factor in the light emission efficiency of an organic light-emitting device. Fluorescent materials have been widely used as the luminescent materials, and phosphorescent materials are theoretically capable of improving emission efficiency by up to 4 times that of fluorescent materials. As such, use of phosphorescent materials in the electroluminescent mechanism is increasing.
However, in organic light-emitting devices using phosphorescent luminescent materials, in most cases cycle life decreases as emission efficiency increases, and emission efficiency decreases as cycle life increases. For example, in a phosphorescent organic light-emitting device having luminance and emission efficiency suitable for use, when luminance is 97%, cycle life is about 100 hours, which is far less than the commercially available level.